When objects (patient, couch, etc) are being transirradiated in computer tomographs, undesired scattered radiation also is produced in addition to the primary radiation required for image calculation. Owing to the slight extent in a z-direction (corresponding to the direction of the gantry axis of rotation) of previous detectors for radiation measurement, it has sufficed to collimate scattered beams in only one beta direction (corresponding to the direction of the beam fan angle) via suitable collimator plate arrangements. Such collimator arrangements are disclosed, for example, in DE 100 11 877 C2.
With the trend toward ever larger detector surfaces in the z-direction, the collimator arrangements can no longer be designed in a beam-delimiting fashion such that they essentially eliminate scattered radiation. Consequently, the influence of scattered radiation is also no longer negligible in the z-direction and must be suppressed by way of suitable measures.
A theoretically possible, two-dimensional collimation in beta and z-directions by way, for example, of pyramidally arranged collimator plate structures can be implemented technically and economically only with great difficulty because of the requisite aspect ratio of greater than 1:20.